Mutations and genetic variationSpec 3.22, 3.23
In short
A mutation is a change in the base sequence of DNA. There is usually extensive genetic variation within a population, and it arises through mutations. Most mutations have no effect on the phenotype, some have a small effect, and rarely a single mutation significantly affects the phenotype. So it is wrong to say that all mutations are harmful.
A mutation is a change in the base sequence of DNA. There is usually extensive genetic variation within a population of a species, and this variation arises through mutations.
Mutations affect the phenotype in different ways:
- Most genetic mutations have no effect on the phenotype.
- Some mutations have a small effect on the phenotype.
- Rarely, a single mutation will significantly affect the phenotype.
Common mistake:Do not write that all mutations are harmful. Most have no effect on the phenotype.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026
Frequently asked questions
What causes variation in a species?
Variation is caused by genes, the environment, or a combination of both. Genetic variation comes from mutation and sexual reproduction, which give individuals different alleles, as with eye colour. Environmental variation is caused by conditions during life, such as diet, climate or injury; for example, plant height can be affected by light.
What is the difference between continuous and discontinuous variation?
In continuous variation, a feature can take any value within a range, such as height or mass, and the results are shown on a histogram. In discontinuous variation, a feature falls into distinct categories with nothing in between, such as sex or flower colour, and the results are shown on a bar chart.
Are all mutations harmful?
No, most mutations are not harmful. A mutation is a change in the base sequence of DNA, and most mutations have no effect on the phenotype. Some have a small effect, and only rarely does a single mutation significantly affect the phenotype. Mutations are the source of genetic variation within a population.
All 4 questions on Variation, mutations and the Human Genome Project
